The present invention relates to one-component alkoxy-functional RTV compositions and more particularly, the present invention relates to a process for the preparation of alkoxy-terminated diorganopolysiloxane polymers which can be utilized to form one-component RTV silicone rubber compositions.
One-component room temperature vulcanizable (room temperature vulcanizable shall herein after be referred to as RTV) silicone rubber compositions are well-known. These compositions can vary depending on the functionality of the cross-linking agent; for instance, alkoxy-functional RTV silicone rubber compositions are disclosed in Beers, U.S. Pat. No. 4,100,129. These compositions comprise, basically, a silanol terminated diorganopolysiloxane polymer, an alkoxy-functional cross-linking agent such as methyltrimethoxysilane and a titanium chelate condensation catalyst. Such alkoxy-functional RTV compositions have the advantage that they are non-corrosive and that they do not give off pungent and irritating odors during care. There are other one-component RTV systems with different functionalities such as, for instance, amine-funcitonality. However, for many applications it is desirable that the systems exhibit fast cure and have non-corrosive properties. Other compositions which do not have fast cure and non-corrosive properties are, for instance, amino functional systems as disclosed in Nitzsche, et al, U.S. Pat. No. 3,132,528 and enoxy-functional systems as disclosed in Tekago, U.S. Pat. No. 3,819,563 and Tekago, U.S. Pat. No. 4,180,642 in which acetone is evolved during the curing of the system. The disadvantage of the amino-functional system is that it gives off obnoxious fumes while curing, and frequently toxic cure by-products. Further, the enoxy-functional RTV system while having the advantageous properties of being fast-curing and non-corrosive, nevertheless, is quite expensive to manufacture. Accordingly, it is desirable to have a fast-curing, non-corrosive and as inexpensive as possible one-component RTV system for many applications in which silicone RTV compositions are utilized.
In this respect the alkoxy-functional system of Beers, U.S. Pat. No. 4,100,129 has some of these properties. However, these compositions have the disadvantage that they are not as fast curing as would be desired. Further, the cure of these compositions is retarded during storage, so that even after a period of storage after manufacture of as short as 2 weeks, the cure properties are affected. Thus, even though these compositions can be produced to have a storage life anhydrously or semi-anhydrously of 6 months to a year and a half or more, nevertheless, in many cases it has been found that after periods of storage, the compositions will be considerably slower curing than is experienced with the compositions immediately after manufacture and they may not cure at all. It has been postulated that this slowing in the rate of cure is caused by a degradation in the alkoxy cross-linking groups in the polymer system caused by free or unbonded hydroxyl groups in the composition. It has also been demonstrated that this deficiency can be corrected by the utilization of a scavenger for hydroxy groups. The scavenger has a functional group or groups which react with the hydroxy groups and bond with them so that they cannot further degrade the alkoxy-functional groups in the polymer system. Accordingly, it has been found out that these compositions as disclosed in White, et al, U.S. Pat. No. 4,395,526 are extremely more efficient, faster curing and more shelf stable than the compositions of Beers, U.S. Pat. No. 4,100,129.
There have been further developments in the art in this area. For instance, see the disclosure of Chung, now U.S. Pat. No. 4,424,157, which discloses the utilization of a cyclic amide as a scavenger. Further, there are the disclosures of Lucas, U.S. Pat. No. 4,483,973, which discloses the use of various adhesion promoters in such systems and U.S. Pat. Nos. 4,513,115 and 4,539,367, which disclose the utilization of various plasticizing additives and various types of fillers in such compositions to make them low-modulus. Further, there is the disclosure of Dziark, now U.S. Pat. No. 4,417,042 which disclosed the utilization of silazane scavengers in such systems. With respect to the silazane scavengers in such systems as disclosed in U.S. Pat. No. 4,417,042, these compounds are purely scavengers and cannot be utilized as integrated cross-linkers. Further, there is the subsequent Patent Application of Beers, et al, Ser. No. 428,038 and now abandoned which discloses the use of alkoxy-functional silazanes which can be utilized either just as scavengers or depending on their functionality, as integrated cross-linkers. Then, there is the Patent Application of Lucas, now U.S. Pat. No. 4,528,324, which discloses the production of such systems continuously by the utilization of a static mixer and a devolitizing extruder.
However, a more pertinent Patent Application as far as the instant case is concerned is the Patent Application of Chung, Ser. No. 427,930. This Patent Application discloses the end-capping of and particularly the efficient and rapid end-capping of a silanol diorganopolysiloxane polymer with a polyalkoxy funcitonal cross-linking agent in the presence of certain catalysts. Although the earlier cases of White, et al, U.S. Pat. No. 4,395,526 disclose as catalysts for such end-capping reactions amine functional compounds, it was the contribution of Chung, now U.S. Pat. No. 4,515,932, to utilize certain types of acids as end-capping catalysts in the reaction of polyalkoxy-functional silane cross-linking agents with silanol terminated diorganopolysiloxane polymers. Such end-capping catalysts were effective irrespective of whether they were utilized with an integrated cross-linker, scavenger or just a cross-linking agent in the reaction. It was also further disclosed in that Patent Application that the most efficient end-capping catalyst is a combination of an acid with an amine-functional compound. Thus, in these reactions the polyalkoxy silane is reacted with a silanol terminated diorganopolysiloxane in the presence of such catalysts which results in a rapid and efficient end-capping reaction. It should be pointed out that such an end-capping reaction is considerably more efficient and results in more of the desired product than is the case with the end-capping reaction of Brown, et al, U.S. Pat. No. Re 29,760. This patent discloses the reaction of alkoxy-functional chlorosilanes with silanol terminated diorganopolysiloxane polymers to produce the desired polyalkoxy terminated diorganopolysiloxane polymer which forms the base of an alkoxy-functional one-component RTV system. Not only is the end-capping reaction more efficient as disclosed in the foregoing Patent Application of Chung, now U.S. Pat. No. 4,515,932, but further, the final product has more advantageous properties; that is, it is more stable and has a faster cure rate and has generally better physical properties than is the case with the Brown, et al, cured composition which is produced as disclosed in U.S. Pat. Re 29,760. It is now generally desirable to disclose another way of producing such polyalkoxy-functional diorganopolysiloxane polymers for utilization as base polymers in the production of one-component RTV systems.
Accordingly, it is one object of the present invention to provide an efficient process for producing a polyalkoxy-functional terminated diorganopolysiloxane polymer which can be utilized to produce one-component RTV systems.
It is an additional object of the present invention to provide a simple but rapid process for the production of alkoxy-terminated diorganopolysiloxane polymers.
It is a still further object of the present invention to provide for alkoxy-functional one-component RTV systems by disclosing a simple but efficient process for production of the alkoxy-functional base polymer utilized in such systems.
These and other objects of the present invention are supported by the disclosures set forth herein below.